|MCBRIDE, MATTHEW - University Of Arizona|
|Carroll, Jeffery - Jeff Carroll|
|ORTIZ, XAVIER - University Of Arizona|
|COLLIER, JAYNE - University Of Arizona|
|CHAPMAN, JAMES - Phibro Animal Health Corporation|
|MCLEAN, DEREK - Phibro Animal Health Corporation|
|KATTESH, HANK - University Of Tennessee|
|COLLIER, ROBERT - University Of Arizona|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 4/21/2016
Publication Date: 7/1/2016
Citation: Mcbride, M.L., Sanchez, N.C., Carroll, J.A., Broadway, P.R., Ortiz, X.A., Collier, J.L., Chapman, J.D., Mclean, D., Kattesh, H., Collier, R.J. 2016. Omnigen-AF reduces basal plasma cortisol, AWA cortisol release to adrencocorticotropic hormone or corticotrophin releasing hormone & vasopressin in lactating dairy cows under thermoneutral or acute heat stress conditions.. Journal of Animal Science Supplement. 94 (E-Supplement 5):531-532, Abstract#1128.
Technical Abstract: Differences in the adrenal cortisol response of OmniGen-AF (OG) supplemented dairy cows to a corticotrophin releasing hormone (CRH) and vasopressin (VP) or an adrenocorticotropic hormone (ACTH) challenge when housed at different temperature-humidity indices (THI) were studied. Holstein cows (n=12; 162+/-1 days in milk) were balanced for milk yield, BW and DIM and randomly assigned to 1 of 2 trts: 1) OminGen-AF, supplemented with OG at 56 g/hd/day for 70d; or 2) Control (CON), no supplement. Cows were moved to individual tie stalls in 1 of 2 temperature controlled chambers on d45 and fitted with indwelling RT devices and jugular catheters on d52. Initially THI was cycling at thermoneutrality (TN; THI<72 for 24 h/d) for 10d, followed by HS (THI>72 for 12h/d) for 10d. Cows were challenged with CRH (0.3 microgram/kg) and VP (1 microgram/kg) at 1000h on d6 of TN (d53 of study) and d1 of HS (d57 of study), and with ACTH (0.1 IU/kg) at 1000h on d7 of TN and d2 of HS. Blood samples were collected from -2 to 8h at 30-min intervals relative to each challenge and analyzed for cortisol and corticoid-binding globulin. Mean plasma cortisol concentration prior to challenge was lower in OG fed cows compared to CON, (9.24 vs 15.80 ng/ml P<0.003). Mean plasma cortisol concentration was also lower in OG-fed cows compared to CON challenged with ACTH during both TN (27.2 vs 43.4 ng/ml, P<0.01) and acute HS (11.2 vs 47.8 ng/ml, P<0.01). Mean plasma cortisol concentrations were numerically lower in OG-fed animals compared to CON infused with CRH-VP during TN (38.2 vs 44.9 ng/ml, P<0.06) and significantly lower than CON infused with CRH-VP during acute HS (49.8 ng/ml vs 78.3 ng/ml, P<0.01). Mean plasma CBG concentration was lower following ACTH infusion than following CRH-VP (753.2 vs 913.3, P<0.01). We failed to detect an effect of OG on plasma CBG concentrations under TN or HS conditions. However, plasma CBG concentrations were elevated by HS in both Con and OG-fed animals following CRH-VP infusion, (1033 vs 795 ng/ml, P<0.01). We conclude that cortisol response to ACTH and CRH-VP was reduced in OG-fed cows compared to CON and this difference was enhanced during acute thermal stress.